1. Field of the Invention
The present invention relates to a technology for enhancing image quality at low image forming cost when more than one page of image data is output on a single page in a combined manner.
2. Description of the Related Art
Typically, from the perspective of image quality or image forming cost, an image processing apparatus such as a copier, a printer, or a multifunction product (MFP) determines whether an original is a color original (i.e., an original having color image data) or a monochrome original (i.e., an original having monochrome image data) and, if the original is determined to be a monochrome original, outputs image data in monochrome. For example, Japanese Patent Application Laid-open No. H9-138608 discloses an image forming apparatus that, depending on the number of color originals in the total number of originals to be output and the user setting, selects a color image-forming mode or a black-and-white (B&W) image-forming mode.
Typically, an image processing apparatus outputs a single image or a plurality of images in a combined manner on a single page. Normally, in the case of one-to-one copying (i.e., copying with identical magnification), a monochrome original is not subjected to color output because the image forming cost for color output is higher than the image forming cost for monochrome output. However, consider a case of two-in-one output (i.e., two pages of image data is combined on a single page) or four-in-one output (i.e., four pages of image data is combined on a single page). In that case, if the originals to be combined include at least one color original, then the originals are subjected to color output and the image forming cost is determined according to the color output.
Japanese Patent No. 3772610 discloses an image forming apparatus that uses halftone dots for determining whether an image data in an original is color image data or monochrome image data, and always outputs monochrome image data in monochrome to enhance the image quality of the combined image data. To perform monochrome output, RGB-to-CMYK conversion (or RGB-to-K conversion) is used such that the final output is in black only. Meanwhile, RGB stands for a color model of red, blue, and green; while CMYK stands for a color model of cyan, magenta, yellow, and black.
However, there is still room for enhancing the image quality at lower image forming cost.
Conventionally, originals determined to be monochrome (B&W) originals are always output in monochrome. That rules out the option of subjecting the monochrome originals to color output for obtaining high-quality monochrome reproduction. Thus, that leaves room for enhancement in the image quality. Moreover, consider a case of combining image data of a plurality of originals on a single page. In that case, even if only one color original is present in the originals to be combined, then all the originals can be subjected to color output and the image forming cost is determined according to the color output. However, the factors such as the image quality and the image forming cost while performing the color output have not been given due consideration in conventional techniques.
In recent times, image processing functionalities such as black character identification have improved vastly. For example, a technology has been developed in which, even if image portion in a monochrome original is output in full-color, character portion is output in a single color output such as black. Moreover, depending on the type or the usage of a monochrome original, sometimes it is desirable not to subject that original to monochrome output. For example, instead of performing monochrome output, if a monochrome original having a picture is reproduced in grayscale using four colors by performing color output, then it becomes possible to ensure proper image density, granularity, and gloss in the output image. Furthermore, to reproduce a high-quality monochrome image, many users are not content with the black color of toner or ink. Such users like to simulate a particular black color with combination of CMYK.
FIG. 10 is a diagram for explaining a conventional technique to combine three originals having monochrome characters and one original having color characters and a monochrome picture on a single page (four-in-one output). In that case, based on an original-type identification result, the three originals having monochrome characters are determined to be monochrome originals; while the remaining original is determined to be a color original. When those four originals are combined on a single page, the image data corresponding to the three monochrome originals is output in monochrome; while the color characters in the color original are output in color and the monochrome picture in the color original is output in grayscale using four colors.
FIG. 11 is a diagram for explaining a conventional technique to combine one original having monochrome characters, two originals having a monochrome picture and monochrome characters, and one original having color characters and a monochrome picture on a single page (four-in-one output). In that case, based on an original-type identification result, only the original having color characters (bottom right original in FIG. 11) is determined to be a color original; while the remaining three originals are determined to be monochrome originals. When those four originals are combined, then all the monochrome originals are output in monochrome; while the monochrome picture in the color original is output in grayscale using four colors and the color characters in the color original are output as color text.
In this way, conventionally, reproduction in grayscale using four colors image is performed only with respect to a color original. That results in a lack of uniformity in the combined output. Moreover, the monochrome reproduction results in relatively low image quality such as poor image density, poor granularity, or less gloss. Furthermore, generally, conventional techniques of combining image data take into consideration only the case of outputting image data on paper. However, with the recent advancement in networking, it is also necessary to take into consideration facsimile transmission or distribution of combined image data over the network.
While determining the output mode (color output or monochrome output) for image data based on an original-type identification result, it is necessary to take into consideration not only the combined image data but also the image forming cost with respect to each output mode. Generally, when all the originals to be combined are determined to be monochrome originals, then each original is output in a monochrome manner because the image forming cost is less than that of color output. However, if there is not a substantial difference in the image forming cost of monochrome output and the image forming cost of color output, then color output should be taken into consideration for enhancing the image quality.